A good form coating should do three things for the contractor who uses it. It should provide a clean release from the concrete; it should protect and extend the life of the form and leave forms free of concrete residue; and it should provide a hard, non-powdery paintable surface, free from stains. The earliest form coatings were simply straight oils of mineral, vegetable or fish origin. Today there are several types of form coatings available to the contractor. Petroleum derivative oils are marketed for formwork use by most of the major oil companies. They provide a simple and effective means for impregnating the external veneer of plywood or a timber surface to eliminate local surface variations in absorbency which could otherwise be reflected in the concrete surface. Waxes and greases may also be used as form release agents and while they provide excellent clean release properties, a straight wax can be used only when temperatures are above 50 degrees F. Oil-phased emulsions consist of water globules encased in a continuous phase of oil. A good oil-phased emulsion will yield concrete which is uniform in color, has minimum staining and good durability, is resistant to efflorescence, and has few mechanical defects, such as pocking and chalking. Volatile coatings, another of the petroleum based products, uses a light petroleum naphtha as the vehicle for various other ingredients. Because the vehicle is evaporative, there is no danger of staining the surface or causing mechanical defects provided the coating is evenly and cleanly applied. Chemically active form coatings take advantage of the free limes that are present in fresh concrete to produce water insoluble soaps. The net result of the action of a soap on the concrete surface is a uniformly high color, a flat finish, and fewer and considerable smaller pock marks than are found with conventional form coatings. The type of form material being used obviously exerts considerable influence on the performance of a form coating. For example, the most important characteristic to be overcome in wood and plywood forms is absorbency, whereas steel forms are completely non-absorbent. The properties needed in a form coating will also differ. For instance, if a plastic sheet form liner or a form of built-up fiberglass is used, there is no need for a releasing agent.